1. Field of the Invention
This invention relates to a method of manufacturing composite sheet materials, in particular laminated sheet materials formed of layers of plastic foam such as expanded polystyrene (EPS). The invention also relates to a sheet material formed by such a method.
2. Related Art
Plastics, and in particular foamed plastics, are employed in great quantities for packaging purposes. Taking the environmental question into consideration, increasing efforts are being made to reuse these materials; that is, to recycle them. Plastics are particularly well suited for reuse in general, but the use of recycled plastics or plastic foam in packaging is inhibited by a number of problems.
On the one hand, the color of recycled plastics material is normally very difficult to alter, and in many cases will not meet requirements. Then there are the obvious psychological and hygienic considerations which apply in particular to the packaging of foodstuffs, especially where the foodstuffs might come into contact with the recycled plastic material.
To preclude any possibility of such contact and yet employ recycled material, it has long been suggested in the packaging arts that a laminate be formed in which a layer or stratum of recycled material is completely covered on at least one side by a layer of previously unused or "virgin" material. More often, to obviate any possibility of contamination or the appearance of contamination, the recycled material is encapsulated in virgin material, or in the case of sheet, foil or film a "sandwich" is formed of an inner layer of recycled material enclosed between two layers of virgin material.
EPS sheet is conventionally formed by extrusion, as by continuously extruding a cylinder or tube of EPS film, expanding the tube under internal air pressure, and slitting the expanded tube or "balloon" at one side and rolling it out to form a single sheet, or slitting it at opposite sides to form two sheets.
It is also known to form a laminate of EPS by simply introducing the extruded tube between a pair of rollers to press it flat, and then continuously trimming the lateral edges from the flattened tube. Just such a technique is disclosed in German Patent Specification No. 2,946,867, published Oct. 27, 1983 in the names of T. Komori et al.
With these considerations as a starting point, the invention addresses the problem of creating by means of a simple method sheet materials which will meet packaging requirements, yet make use of recycled plastic.